This invention relates to a method for efficiently separating water from hydrocarbons under surfactant conditions. More particularly, the present invention is directed to a method of separating a discontinuous phase of water from continuous phase hydrocarbons, such as aviation jet fuel, kerosene, gasoline, diesel fuel, and light cycle oil under the presence of a surfactant such as the thermal stability additive disclosed in U.S. Pat. No. 5,596,130.
U.S. Pat. No. 5,596,130
Turbine combustion fuel oils are used as a heat sink in integrated aircraft thermal systems to cool aircraft subsystems and the engine lubricating oil. The turbine combustion fuel oil is circulated in the airframe to match heat loads with available heat sink. In current aircraft, these thermal stresses raise bulk fuel temperatures to as high as 425xc2x0 F. at the inlet to the main burner fuel nozzles and above 500xc2x0 F. inside the fuel nozzle passages. In future aircraft, these temperatures are expected to be 100xc2x0 higher.
At these high temperatures and oxygen-rich atmospheres in aircraft and engine fuel system components, fuel degrades forming gums, varnishes, and coke deposits. These deposits plug-up the components leading to operational problems including reduced thrust and performance anomalies in the augmentor, poor spray patterns and premature failure of main burner combustors and problems with fuel controls. Further, the engine exhaust becomes smoky and sooty and engine noise increases, both of which are undesirable characteristics for jet engines.
An economical solution to inhibit deposit formation is to add additives to the turbine combustion fuel oil prior to their combustion as propulsion fuels. As indicated in U.S. Pat. No. 5,596,130, it was found that the existing deposits are efficiently inhibited and removed by the addition of derivatives of polyalkenyl (thio) phosphonic acids to the turbine combustion fuel oil. Likewise, the formation of exhaust soot and smoke is inhibited and engine noise reduced.
JP8+100 Fuel
The U.S. military""s newly developed jet fuel, JP8+100, is for use in the next generation of military aircraft. The new fuel with thermal stability additive not only increases thermal stability of jet fuel, but also largely reduces the maintenance costs of aircraft engine due to the fact that a thermal stability additive can inhibit the formation of fouling deposits on engine components. However, the traditional design water/fuel coalescers utilizing fiberglass materials are disarmed by surfactant type thermal stability additive, and therefore, fail to pass performance requirements (refer to American Petroleum Institute 1581 Specification, Fourth Edition). Hence, in order to develop a novel coalescer design with surfactant insensitive media to successfully separate water from fuel JP8+100, it is important to understand the effect of thermal stability additive on coalescence and the disarming mechanism of the conventional fiberglass coalescer.
The Disarming Mechanism of Conventional Coalescer
The disarming mechanism for traditional fiberglass coalescer by additives involves two considerations. (1) Surfactants can remarkably reduce interfacial tension, stabilize an emulsion, and even form a micro-emulsion resulting in tiny water droplets ranging from 0.01 to 0.2 xcexcm. This stable micro-emulsion will make coalescence very difficult. (2) The polar head of surfactants can be adsorbed or coated on the hydrophilic site of certain fibrous media such as fiberglass. On the other hand, the straight chain hydrocarbon tail of surfactants, having both hydrophobic and oleophilic properties, can make the fiber surface completely change wettability from hydrophilic to hydrophobic, since surfactants have more affinity than water. Water droplets will not be captured by the wettability of fiber surface. Therefore, surfactants can disarm the fiber glass coalescers by combining the above two effects.
Prior Art to Filter Under [Strong] Surfactant Conditions
There are two conventional ways to remove water from hydrocarbon based fluids with surfactants present.
1) The first method uses a two-stage system including a clay treater and conventional coalescer. After surfactants in hydrocarbon fluids are removed by the clay treater, then the conventional coalescer is used to remove water. The clay treater consists of diatomaceous earth which can adsorb surfactants. Such treatment however, will remove all surfactants: desirable and undesirable. For example, thermal stability additive in JP8+100 fuel is the desirable surfactant for ensuring thermal stability and reducing maintenance. Another apparent drawback for a clay treater is that it can be disarmed by a large amount of water. Hence a clay filter is not feasible for this application.
2) The second method employs an absorption type filter to absorb water within the structure of its hydrophilic absorbing polymer. Even though filters with absorption media can effectively eliminate water from hydrocarbons under the presence of surfactants, they have limited life due to the saturation capacity of their media. Especially for the conditions such as hydrocarbon fluids with high water content e.g. 3% water, absorbing type filters will reach the saturation limit in a short period of time. Therefore, flow will be forced to shut down and the filter must be replaced.
In summary, both methods have significant disadvantages: the former removes desirable surfactants and the latter is not economically feasible.
Novel Coalescer Media
With specially formulated novel media, the novel coalescer system can overcome the negative effect caused by surfactants (e.g. thermal stability additive), such as lower interfacial tension, coating of fiber surface, uncontrolled wettability and stabilized microemulsion. This design can simultaneously and efficiently remove water and solid contaminants from hydrocarbon fluids containing surfactants, such as JP8+100 fuel, with long service life.
Conventional Mechanisms of Coalescence
The conventional mechanism of coalescence in a fibrous bed is explained by the Hazlett model. The model consists of four main steps: (1) Approach of a droplet to a fiber, (2) Attachment of the droplet to the fiber, (3) Coalescence of attached droplets on the fiber, and (4) Release of enlarged droplets from the downstream side of the fiber bed. Thus, coalescing water droplets from the hydrocarbon phase requires a hydrophilic site in a fibrous bed in order to attach water droplets to fibers. The glass fiber medium applied in conventional coalescer device has a surface which has both hydrophilic (silanol group) and hydrophobic (organic resin) regions. It is widely accepted that water interception and growth occurs at the hydrophilic sites. When the surfactants are present, the polar head of the surfactant can also be adsorbed at the hydrophilic sites. Such a process causes disarming of the coalescer unit. This coating phenomena of fiber surface by surfactant has been evidenced by using Environmental Scanning Electron Microscopy (ESEM). See Hughes, V. B., 2nd International Filtration Conference, Apr. 1-2, 1988.
Numerous references disclose multiple layer coalescers including a pleated fiber glass layer. For example, WO 98/14257 discloses a multiple layer (10,20) coalescer including a coalescing media 10 which may be comprised of glass fibers (see page 5, line 17) and which may be pleated (see page 5, line 13). The WO 98/14257 publication also discloses that coalescing media 10 may be comprised of polyester.
U.S. Pat. No. 5,480,547 discloses a multiple layer coalescer including a glass fiber layer (see column 6, line 18) and a fibrous polyester layer (see column 6, line 67).
U.S. Pat. No. 4,892,667 teaches a multiple layer coalescer including a pleated paper layer (see column 3, line 57), and also including a polyvinyl chloride coated screen 75 (see column 6, line 33).
U.S. Pat. No. 4,888,117 discloses a coalescer cartridge comprising a polymeric media having a fine porous structure which may be fabricated from a suitable polymeric material such as polyethylene or polypropylene (see column 1, line 65-68).
U.S. Pat. No. 4,102,785 describes a filter tube including an open scrim sheet material embedded within a wall of the filter tube. The filter tube may be comprised of a plurality of nonwoven fibers having interstices defining a porous filter.
The present invention is directed to a coalescing filter element for the separation of water from hydrocarbon fluids under surfactant conditions. It overcomes many of the shortcomings of conventional methods of removing the aqueous phase from a hydrocarbon phase in the presence of surfactants. The presence of surfactants can disarm the conventional coalescer element in two ways, as noted previously: (1) surfactants reduce interfacial tension and form a stable microemulsion to prevent coalescence, (2) surfactants can be adsorbed or coated on the fiber media, and change its characteristics such. as wettability. Such a process can disarm the coalescence action. The present invention discloses a novel coalescer media which is resistant to surfactant coating, and provides a new coalescer device to successfully remove dirt and water from hydrocarbon fluids.